Ancient gardener, one maybe working very hard (7)
I believe the answer is:
adamant
'hard' is the definition.
(thesaurus)
'ancient gardener one maybe working very' is the wordplay.
I cannot quite see how this works, but
'gardener' could be 'adam' (I've seen this before) and 'adam' is found within the answer.
'one' could be 'an' (I've seen this in other clues) and 'an' is located in the answer.
A single letter 't' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for adamant that I've seen before include "Impervious to pleas or persuasion" , "Unswerving" , "Hard stone" , "uncompromising" , "Hard and unrelenting" .)